King Charles III slammed Prince Harry as “that fool” after the release of his savage 2022 Netflix tell-all docuseries “Harry and Meghan,” a new book claims.

According to Omid Scobie, who wrote the high-anticipated “Endgame: Inside the Royal Family and the Monarchy’s Fight for Survival,” Charles, 75, went from not wanting anyone to discuss his estranged son to openly mocking him.

“[The Netflix series] took the wind out of everyone’s sails,” an unidentified royal aide told Scobie. “[Charles] went from not wanting anyone to talk about his son to openly criticizing ‘that fool.’ ”

Revelations from the six-episode series include allegations that Charles’ office leaked Harry and Meghan Markle’s planned move to Canada, which was later scrapped.

“At the Palace, heads were in hands and migraines were brewing,” added Scobie, 42.

The Post reached out to Buckingham Palace and Harry, 39, reps for comment.

Scobie’s book, due out Tuesday, also claims that Prince William and Kate Middleton, both 41, found the portrayal of Harry and Markle, 42, in the raunchy TV show “South Park” to be “hilarious.”

In “The Worldwide Privacy Tour” episode, which aired in February, the couple was parodied as the Prince and Princess of Canada.

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Their appearance at the funeral of the queen of Canada — who bears a striking resemblance to the late Queen Elizabeth II — is met with anger.

The cartoon couple move to South Park — mirroring the real-life royals’ decampment to California — where they embark on a “Worldwide Privacy Tour,” which consists of the pair shooting off fireworks and playing drums on their front lawn as they display signs that read, “Stop looking at us” and “We want our privacy!!”

Scobie’s book also paints Charles as a “pampered” figurehead who reportedly requires 1,000-thread-count bedsheets when he travels, as well as someone to tie his shoes for him.

The book reports that Middleton and Markle, meanwhile, were encouraged by palace staffers to dress like the late Princess Diana.

“While finding a trend untouched by Diana’s iconic style is almost impossible, the huge amount of effort that goes into channeling her exact look sometimes goes beyond the pale,” Scobie wrote.

“During the past 13 years, Diana cosplay has become a royal staple,” he added.

Even so, the decision to dress the Duchess of Sussex and the Princess of Wales was “always discussed with [William or Harry].”

“At the right moment this can be a sweet gesture,” an unidentified royal insider told Scobie of the directive to reproduce Diana’s fashion. “But there is also a slightly queasy feeling when you realize it’s often orchestrated within the same system that contributed to her living misery, and an institution that still wants some of Diana’s shine to rub off on them.”